The invention relates to a hydraulic jackknifing-controlling apparatus provided with hydraulic damping for articulated vehicles, in particular to rear-engined push-type articulated bussed.
It is a well known fact that with a rear-engined push-type articulated bus an apparatus for controlling jackknifing is desired in order to prevent irregular motion of the trailer. As a consequence of push forces arising from the driven wheels of the trailer, the rear-engined push-type articulated bus tends to jackknife toward the inside of a curve, as well as to be carried toward the outside of the curve if it is travelling at high speed. These phenomena can be controlled by means of jackknifing controlling apparatus, which tends to block improper articulation while permitting normal articulation.
The aim of application of any jackknifing controlling apparatus is to prevent dangerous motion of the vehicle without affecting normal motion. With the articulated bus of German DE-AS No. 2,420,303 (corresponding to the Hungarian Pat. HU-PS No. 177,521) the articulated blocking device will be actuated if the angle of the steered wheel and the angle of articulation are of opposite direction and if the angle of articulation is larger, than 5.5.degree..
Furtheron, to prevent jackknifing, the articulation will be blocked, if the angle of articulation is larger, than 5.5.degree. and simultaneously it is larger than indicated by the angle of the steered wheels. The apparatus functions to damp lateral swinging of the trailer if the angle of the steered wheel is within the range of .+-.8.degree. and the angle of articulation remains within the range of .+-.5.5.degree..
In accordance with patent application EU-0046,484, a built-in shock-absorber is unidirectionally operative. If compressed, its resistance is proportional to the speed of the piston, while the piston is relatively free to move in an extending direction. No externally controlled regulator is built in into the shock-absorber.
Experimental and plant experiences having been gained with rear-engined push-type articulated busses show that with higher travelling speeds, over 80-100 km/h, the trailer begins to swing as a consequence of a sudden movement of the steering or due to a sudden change in push force, or while changing the lane of traffic.
Proposals according to earlier patent specifications try to solve the problem in different ways. In systems with an hydraulic blocking piston, it seems to be obvious to build-in a flow reistance for damping, i.e. to apply a changeable resistance. In accordance with the Hungarian Pat. No. HU-PS 179,667 (U.S. Pat. No. 4,366,966; SU-PS No. 1,032,997) the extent of flow resistance increases with the magnitude of the articulation angle. However, with the solution according to the DE-OS No. 3,004,409, resistance is not a function of the change of the angle of articulation. For the control of flow resistance--which can be connected and disconnected--the latter specification proposes consideration of travel-dynamic characteristics differing from each other. According to one of the proposed solutions flow resistance can be adjusted to a low value at small angles of steering. According to another proposed solution damping resistance can be adjusted to a high value with low angles of steering, if the speed of travel is high. So the specification does not give a definite guidance in respect to the adjustment of the extent of damping for rear-engined push-type articulated busses with hydraulic jackknifing-blocking systems.
Resulting from the complicated travel dynamic characteristics of an articulated vehicle, it becoems apparent that lateral irregular swinging of the trailer cannot be correctly prevented while ignoring any of the fundamentally important travel-dynamic characteristic, as e.g. angle of the steered wheel (HU-PS No. 179,667) or angle of articulation (DE-OS No. 3,004,409), or where the extent of damping is correlated exclusively with the rate of change of the angle of articulation.
The aim of our invention is into develop a jackknifing-damping apparatus, which is able to prevent lateral swinging of the trailer by its damping effect and which promotes in a most efficient manner decay of the swinging process within the shortest time. The system of the invention takes into consideration the angle of articulation and its difference with respect to direction and magnitude compared to a predetermined optimum angle of articulation for a particular angle of the steered wheels. The new system actuates accordingly a changeable hydraulic resistance, which exerts a resisting moment proportional to angular speed of jackknifing. Shock absorbtion requires substantial flow resistance. At the same time, jackknifing motion taking place with the slip-free rolling of the vehicle wheels requires minimum throttling. The solution according to the invention for meeting these contradictory requirements is based on the recognition that an optimal angular speed of jackknifing motion is proportional to the difference between the actual angle of articulation and the ideal angle of articulation for the momentary angle of the steered wheels. Angular speed of optimal jackknifing motion is also directly proportional to the speed of advance of the articulated vehicle. As we do not desire to prevent optimal jackknifing motions, the extent of flow resistance should be inversely proportional to the difference between the actual angle of articulation and the ideal angle of articulation according to the momentary angle of the steered wheels. In addition, it is expedient to influence the magnitude of resistance inversely proportionally to the travelling speed of the articulated vehicle.
In accorance with the invention, the objective is achieved by utilizing with the jackknifing-affecting apparatus according to the Hungarian Patent HU-PS No. 182,445 (U.S. Pat. No. 4,344,640, DE-AS No. 3,031,601), an electronic apparatus for sensing and evaluating the angular position, which determines the difference between the actual angle of articulation and the ideal angle of articulation indicated by the angle of the steered wheels and providing a corresponding output signal. Such output signal is processed in an electronic throttle control unit and, as a function of the magnitude of deviation, it actuates a changeable and/or connected-disconnectable resistance arranged in a common hydraulic circuit with blocking cylinders. In one embodiment, flow resistance is controlled so that the curve of the angle of articulation ideally related to the angle of the steered wheels is enclosed by a controlling zone, within which a resistance-increasing unit becomes actuated. For angles of articulation lying outside this zone, the resistance device is set to a minimal flow resistance with the aim, that the trailer can approximate a regular jackknifing positon relatively small resistance. Prior to reaching this state, i.e., within the aforementioned zone of control, the device increases the flow resistance effect and this is exerts resistance against the movement of the trailer.
The system of our invention includes a unit for assessing the negative or positive deviation of the actual angle of articulation from the ideal angle of articulation indicated by the angle of the steered wheels. The positive or negative differential signal forms the input signal for the blocking/damping control unit of the equipment. There is also an hydraulic loop sensing the direction of flow in the hydraulic system. In addition, there is an electronic unit the output signal of which represents the extent of deviation of the actual angle of articulation from the ideal angle of articulation indicated by the angle of the steered wheel. This signal forms an input signal to a control for the damping unit. The damping unit has a changeable flow resistance in the hydraulic loop. It is provided with a flow resistor which is changing continuously and/or gradually in an extent which is inversely proportional to the deviation of the actual angle of articulation from the ideal angle of articulation.
In a preferred embodiment of the invention the control zone, enclosing the curve of the ideal angle of articulation in relation to the angle of the steered wheel, has a changing width and it occupies an asymmetric position in relation to the curve of the ideal angle of articulation.
To achieve safe and simple sensing and evaluation, the sensor for sensing the angle of the steered wheel and the sensor of the angle of articulation are formed with discs according to the Gray code and reading means related thereto.